In Oracle Bpel 10g we had the functionality to add preferences to your bpel process.
By adding the next xml to the bpel.xml file we could get the value as variable into our process and change the value from the console.

Now we can use the function ora:getPreference(myPref) in our bpel process to retrieve the value of the preference.
Watch the naming convention. It expects it to start with “bpel.preference”.

Create the composite application and deploy it.
We only added an assign to the flow which will get assign the value of the preference to the outputVariable.
Run the bpel and check if the value of ‘MyCurrentValue’ is in the outputVariable.

In Oracle SOA Suite 10g we could change the value of the preferences from the bpel console.
In Oracle SOA Suite 11g things changed a but, we got a new fancy console to manage all the components.
To change to values from the prefences go to the ‘Enterprise Manager’ (http://localhost:7001/em).

* Addition
There were some questions on how to persist the new value of the preference after server restart

After clicking ‘Apply’ click ‘Return’.
Go to the ‘Operations’ tab and click on the ‘save’ operation. Click ‘Invoke’ and ‘Return’
If you now restart the service the changed value of your preference with still be there.

Are you retrieving the property from within your bpel process the correct way?
The definition of the property looks ok, so the getPreference function should work.
Can you paste the bpel code from which you do the get ?